Hard Decisions Ahead
With Ash Trees
By: Stanton Gill,
Extension Specialist in IPM and Entomology for Greenhouses and Nurseries
Central Maryland Research and Education Center
University of Maryland
Protect it or cut it down? This decision is one
that managers are going to be faced with over
the next couple of years where there are green
or white ash planted in the landscape. Green
and white ash were one of the top selling
nursery trees for over 40 years and a lot of
them were installed in new communities
around office parks throughout the metro area.
Many of these trees are now big caliber trees
of 15 – 25” DBH. You heard the saying “The
bigger they are, the harder they fall”. This case
will be very true in many landscapes.
In May 2013, a meeting was organized to help
city managers and arborists understand what
we can expect as emerald ash borer continues
to establish itself in Maryland. The program
organizers brought in urban forester managers
from mid-west cities that had to deal with the
fall of the ash in the mid-west. They commented that you go through about 3 or 4 years of
discovery of the pest in the area followed by a tidal wave of dying trees. This is called the
Exponential Death of Trees. You really need to start planning in these early stages because when
the Exponential Death of Trees starts, you will have a large number of dead trees that have to be
taken down.
If you can keep your ash trees alive through the tidal wave, then the population goes down and
you are hopefully left with standing trees. The questions are how much are you are willing to
spend on protecting the ash trees and for how long? There is no natural resistance to the emerald
ash borer among ash trees so the choice is which chemical you apply to the tree to protect its life.
You also have to decide when the tree is taken down. Sounds simple, but as many things in life,
it is not simple at all. A big tree not only shades areas reducing temperatures in summer, it
absorbs huge amounts of runoff water. Taking down a large tree is going to dramatically change
the environment in the area where it was growing. It is also expensive to remove a tree and
stump grind out the roots. A replacement tree takes years to grow and fill in an area. Do you
inject and save the ash or cut it down? I lean toward removing the tree and starting over with
another species of tree but it can be argued it is best to inject and save a tree a little while longer
until the tidal wave passes by. The other thing is it may be too expensive to take down all of the
ash trees in an area preemptively.
Some city foresters are choosing to go out and rate the quality of the ash tree and evaluate its
potential hazard if it dies. They rate the trees on a scale of say 1 – 5 with 5 being the trees that
should have priority on being removed. One city in Maryland that has 22,000 ash trees in its tree
inventory is choosing to remove 500 ash trees each year, picking the ones with a ‘5‘rating. They
are injecting 25 - 30% of the better ash trees to give them more breathing room before these trees
have to be removed. Eventually, the plan is to replace the ash trees with other species of trees
and have a mixed species stand of trees to protect against outbreaks of other insects coming in
the future. This approach is probably the best long range way of dealing with EAB.
The adult beetles will be out in May. Emerald ash borer adults emerge at 450 degree days which
is the time when black locust trees are in full bloom. If you are taking action with insecticide
treatments, then May and June is the best treatment time for most of the treatments.
Adult emerald ash borers range from
iridescent green to greenish copper in color
Here is a list of chemicals with time of application and how long they will give control of the
emerald ash borer:
Table 1. Insecticide options for professionals and homeowners for controlling EAB that have
been tested in multiple university trials. Some products may not be labeled for use in all states.
Some of the listed products failed to protect ash trees when they were applied at labeled rates.
Inclusion of a product in this table does not imply that it is endorsed by the authors or has been
consistently effective for EAB control.
This table is adapted from the publication “Insecticide options for Protecting Ash trees from
Emerald Ash Borer” by Daniel A. Herms et.al. at:
http://emeraldashborer.info/files/multistate_eab_insecticide_fact_sheet.pdf
Insecticide Formulation
Active Ingredient
Application Method
Recommended Timing
Professional Use Products
Mid-fall and/or mid- to late
spring
Mid-fall and/or mid- to late
spring
Merit® (75WP, 75WSP, 2F)
Imidacloprid
Soil injection or drench
XytectTM (2F, 75WSP)
Imidacloprid
Soil injection or drench
IMA-jet®
Imidacloprid
Trunk injection
Early May to mid-June
Imicide®
Imidacloprid
Trunk injection
Early May to mid-June
Emamectin
benzoate (restricted
use)
Trunk injection
Early May to mid-June
Inject-A-Cide B®
Bidrin®
Trunk injection
Early May to mid-June
SafariTM (20 SG)
Dinotefuran
Systemic bark spray
Early May to mid-June
Transtect
Dinotefuran
Soil Injection or Basal
Drench
Early May to June
Astro®
Permethrin
OnyxTM
Bifenthrin
Tempo®
Cyfluthrin
Preventive bark and foliage
cover sprays
2 applications at 4-week
intervals; first spray should
occur when black locust is
blooming (early May in
southern Ohio to early June
in mid-Michigan)
Trunk Injection
Typical application takes 30
-60 minutes per tree.
Translocate throughout the
tree within 48 hours
May to Mid-June
TREE-ägeTM
Sevin® SL
TreeAzin
Carbaryl
Azadirachtin
Homeowner Formulation
Bayer AdvancedTM Tree &
Shrub Insect Control
Imidacloprid
Soil drench
Mid-fall or mid- to late
spring
Table 2. This is a table to help you understand how long each of the soil, bark spray or injection
treatments will provide control of EAB and approximately what professionals are charging to
treat trees per each inch of DBH (diameter at breast height). This is not the actual cost of the
chemical, but is the range of what most certified pesticide applicators are charging to make an
application to a tree.
Imidacloprid
Dinotefuran
Emamectin
benzoate
TreeAzin
Application method
Soil drench or
Injection
Basal trunk spray or
soil injection or
drench
Trunk
Injection
Trunk
Injection
Time of application
Fall or May June
May - June
May - June
May - June
Residual control
1 year
5 – 7 months
2 years
2 years
What most applicators
charge to treat per 1
inch of DBH
$1 - $5
$10- $15
$10 - $15
$20 - $30
In Canada they have severely restricted the chemicals that can be used for insect control. The
Canadian Forest Service has backed the development of a 5% Azadirachtin B marketed by
BioForest Technology, Inc (Distributed in the US by Rainbow TreeCare) for tree injection that
should satisfy the organic type customer. The product is called TreeAzin systemic insecticide.
This product is an organic systemic insecticide (OMRI listed) for control of Emerald Ash borers.
The Azadirachtin that is extracted from Neem tree seeds acts as an Insect Growth Regulator. The
larvae are prevented from completing development and die before they can go to the next instar
(growth) stage. When treating with TreeAzin for control of EAB, it is suggested to use between 5
to 18.5 ml per DBH. It has been tested in Canada and is supposedly providing 95% control of
EAB larvae. Testing in the United State started in 2013.
The product must be stored at 40 – 70 °F and will last one year in storage. When you take it out
to the field, it is recommended that you pack the material in a cooler with ice packs to keep it
cool. The formulation is very thick and it is injected using large tubes and takes 30 - 60 minutes
to get it into the trees.
Back to What to Do
In May 2013, the city forester from Fort Wayne, Indiana was asked to come and address arborist
and landscape managers on how they dealt with EAB in their city. Chad Tickle, the city forester,
started with the comment “As the population of EAB goes up the options go down”. His
approach is to remove a certain number of ash trees each year and treat a set number of trees to
buy time until you have to take the trees down. There just isn’t enough money to take all of the
ash trees down in most cities on one year’s budget. He mentioned that it we are in the early
stages in most of Maryland, and you can get lulled into thinking you don’t need to do anything.
Doing nothing is a bad decision because in 2 - 3 year you are suddenly faced with many
standing, but dead ash trees.
During the meeting Nevin Dawson, forestry expert, University of Maryland Extension,
commented that the City of Baltimore has over 300,000 ash trees in the city. Baltimore is one
city in Maryland that better start developing a plan for dealing with EAB soon.
In Fort Wayne, when Chad started in his job in 2008, there were 59,000 street trees in the city
limits. In 2013 they have 46,000 trees in the city limits. The reduction in tree numbers is mainly
due to the removal of ash trees. They still have ash standing, but not many. Green and white ash
trees were 25% of the Fort Wayne city tree plantings in 2008. They started their management
program with a tree inventory to know what they have and where the trees are located. They then
evaluated the tree health and determined which trees needed to be removed immediately and
which trees could be treated with imidacloprid to give them one year of control and at least 2
more years until the tree would be killed by EAB and have to be removed. It is a buying time
strategy. Originally in Fort Wayne, they treated 11,000 trees with soil injection of imidacloprid
to buy time. Now, they treat 1300 trees per year. Chad also noted that emerald ash borers seem to
like green ash the most with white ash being less preferred, but it still will be attacked. Chad told
the group that the 14,000 trees in Fort Wayne has cost $7.2 million to take down and treat from
2008 – 2013. Even with this aggressive plan it is not enough for many people and Chad still
receives in over 250 complaints about dead or dying trees in the city from citizens who want
immediate action to remove the dead trees in their neighborhood. He said you better be
organized and prepared. It is good advice for us here in Maryland. We are not trying to scare
anyone with this article, but you need to make sure your clientele understand the choices and the
consequences of “no action”.
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